This invention relates to an adhesive composition used in hot melt adhesives and solvent-based adhesives. More particularly, it relates to vinyl aromatic hydrocarbon/acrylic monomer block copolymer adhesive compositions.
It is known that a block copolymer can be obtained by an anionic copolymerization of conjugated dienes or such dienes and an alkenyl arene compound by using an organic alkali metal initiator. For example, block copolymers have been produced which comprise primarily those having a general structure EQU A-B and A-B-A
wherein the polymer blocks A comprise thermoplastic polymer blocks of alkenyl arenes such as polystyrene, while block B is a polymer block of a conjugated diene such as polybutadiene or polyisoprene. They may be linear, radial, star, tapered and/or asymmetric and hydrogenated or unhydrogenated. The proportion of the thermoplastic blocks to the elastomeric polymer block and the relative molecular weights of each of these blocks is balanced to obtain a rubber having unique performance characteristics.
It is well known that these polymers are useful in formulating adhesives. Such polymers are especially useful in formulating adhesives that are superior in adhesion to nonpolar surfaces. Styrene-isoprene-styrene block copolymers are known to be especially useful as such. They are commonly used in combination with an S-I block copolymer to increase tack. Acrylic adhesives are known to be useful for making adhesives that are superior in adhesion to polar surfaces such as steel, presumably because of favorable energetics between the polar acrylic functionality and the surface polarity. Statutory Invention Registration H1251 entitled "Acrylic-Containing Diene Copolymers in Adhesives, Sealants and Coatings" provides a hot melt adhesive composition which is based on a rubbery or elastomeric acrylic monomer-containing polymer which has superior adhesion to polar surfaces. The present invention provides an adhesive composition with a vinyl aromatic hydrocarbon/diene/acrylic monomer block copolymer which provides better adhesion to Kraft paper while retaining the advantageous properties of SIS block copolymers in adhesives: high shear, aggressive tack, high peel, adhesion to non-polar surfaces, etc.